class Compiler {
  constructor(vm) {
    this.el = vm.$el;
    this.vm = vm;
    this.compile(this.el);
  }
  //编译模板，处理文本节点和元素节点
  compile(el) {
    let childNodes = el.childNodes; //childNodes是一个伪数组
    Array.from(childNodes).forEach(node => {
      if(this.isTextNode(node)) { //处理文本节点
        this.compileText(node);
      } else if(this.isElementNode(node)) { //处理元素节点
        this.compileElement(node);
      }

      //判断node节点是否有子节点，如果有子节点，递归调用compile处理子节点
      if(node.childNodes && node.childNodes.length) {
        this.compile(node);
      }
    });
  }
  //编译元素节点，处理指令
  compileElement(node) {
    //遍历所有的属性节点
    Array.from(node.attributes).forEach(attr => {
      let attrName = attr.name;
      if(this.isDirective(attrName)) {
        attrName = attrName.substr(2);
        let key = attr.value; 
        this.update(node, key, attrName);
      }
    });
  }
  //根据attrName处理指令
  update(node, key, attrName) {
    const index = attrName.indexOf(':');
    if(index !== -1) { attrName = attrName.substr(0,2); }
    let updateFn = this[attrName + 'Updater'];
    updateFn && updateFn.call(this, node, this.vm[key], key);
  }
  //处理v-text指令
  textUpdater(node, value, key) {
    node.textContent = value;
    new Watcher(this.vm, key, (newValue) => { node.textContent = newValue});
  }
  //处理v-model指令
  modelUpdater(node, value, key) {
    node.value = value;
    new Watcher(this.vm, key, (newValue) => { node.value = newValue });
    //双向数据绑定
    node.addEventListener('input', () => { this.vm[key] = node.value });
  }
  //处理v-on指令
  onUpdater(node, value, key) {
    node.addEventListener('click', () => { this.vm.$options.methods[key]() });
  }
  //处理v-html指令
  htmlUpdater(node, value, key) {
    node.innerHTML = value;
    new Watcher(this.vm, key, (newValue) => { node.innerHTML = newValue });
  }
  //编译文本节点，处理差值表达式
  compileText(node) {
    let reg = /\{\{(.+?)\}\}/;
    let value = node.textContent;
    if(reg.test(value)) {
      let key = RegExp.$1.trim(); //获取差值表达式
      node.textContent = value.replace(reg, this.vm[key]);
      
      //创建watcher对象，当数据改变时更新视图
      new Watcher(this.vm, key, (newValue) => { node.textContent = newValue});
    }
  }
  //判断元素属性是否是指令
  isDirective(attrName) {
    return attrName.startsWith("v-");
  }
  //判断节点是否是文本节点
  isTextNode(node) {
    return node.nodeType === 3;
  }
  //判断节点是否是元素节点
  isElementNode(node) {
    return node.nodeType === 1;
  }
}